In offshore production of hydrocarbons (oil and gas) it is known to use production vessels based on the so-called STP technique (STP=Submerged Turret Production). In this technique there is used a submerged buoy of the type comprising a central bottom-anchored member communicating with the topical underground source via at least one flexible riser, and which is provided with a swivel unit for the transfer of fluid under a high pressure to a production plant on the vessel. On the central buoy member there is rotatably mounted an outer buoyancy member which is arranged for introduction and releasable securement in a submerged, downwardly open receiving space at the bottom of the vessel, so that the vessel is able to turn on the anchored central buoy member under the influence of wind, waves and water currents. For a further description of this technique reference may e.g. be made to Norwegian laying-open print No. 176 129 and to international patent application No. PCT/NO94/00119.
In offshore loading and unloading of hydrocarbons it is also known to use a so-called STL buoy (STL=Submerged Turret Loading) which is based on the same principle as the STP buoy, but which has a simpler swivel means than the STP swivel which normally has several through-going passages or courses. For a further description of this buoy structure reference may e.g. be made to international patent application No. PCT/NO92/00056.
By means of the STL/STP technique there is achieved that one is able to carry out loading/unloading as well as offshore production of hydrocarbons in nearly all weathers, a connection as well as a disconnection between vessel and buoy being able to be carried out in a simple and quick manner, also under very difficult weather conditions with high waves. Further, the buoy may remain connected to the vessel in all weathers, a quick disconnection being able to be carried out if a weather limitation should be exceeded.